Chromatic adaptation allows humans to interpret a color within the context of its surroundings. For example, an object such as a red apple may be viewed under different lighting conditions such as sunlight or different colors of artificial light. Even though the illuminant may be different in each situation, the human visual system will indicate that the object has about the same color—the apple will still appear to be red or at least a shade of red.
In situations where color interpretation is carried out by machines, such as when an image is scanned by a scanner and printed by a printer, automatic chromatic adaptation is not performed as in the human visual system. For example, the scanning may take place under a fluorescent light (which contains a lot of bluish light) but the printed image may be viewed under sunlight (which contains a lot of yellow light). Because of the difference in illuminants, chromatic adaptation between the source (the scanner) and the destination (the printer) is needed in order to convey the correct colors into the printed image.
The human visual system perceives the colors in an image or video based on the color of the illuminant at the source (the color of the light under which the image was captured) as well as the color of the light at the destination (the color of the ambient light where the image or video is being viewed). For example, a mobile device may be carried from room to room, with each room illuminated by different types/colors of lights: one room may be lit with artificial incandescent light, the next room with daylight, and another room with artificial mercury-based neon light (a bluish light). Under these conditions, the same image on the device's screen will look different in each room of the various rooms. Thus, while a human may perceive an apple as being red even when viewed under different color lighting conditions because of chromatic adaptation, when an image of a red apple in sunlight is viewed under artificial incandescent light, the apple may not appear to be red or at least may not appear to be the same color of red that would be perceived if the image was instead viewed under the same lighting conditions in which the picture was taken (that is, in sunlight).